Copy Constructor

[bhadrisn]

Hello,

I have a class A. I have a copy constructor inside that class.

From the main function i am calling the copy constructor like below.


A a;
A b = a;

Now whenever the compiler comes to the statement A b=a. how does this work.

My doubt is whether the object b will be created first and a will be copied to b?

Regards,
Bhadri

[Girish Kanakagiri]

Hello,

I have a class A. I have a copy constructor inside that class.

From the main function i am calling the copy constructor like below.


A a;
A b = a;

Now whenever the compiler comes to the statement A b=a. how does this work.

My doubt is whether the object b will be created first and a will be copied to b?

Regards,
Bhadri

From your statements

A a;
A b = a;

It is clear that object a is created first. In the second statement object b is created by passing object "a" as a parameter to the copy constructor. It is converted in this fashion A b(a);

If you don't want this automatic conversion, then supply keyword "explict" for
the constructor so that it stops from such automatic conversions.

If you think, I have answered to your question then don't forget to close this
thread.

Regards,
Girish.

[bhadrisn]

From your statements

A a;
A b = a;

It is clear that object a is created first. In the second statement object b is created by passing object "a" as a parameter to the copy constructor. It is converted in this fashion A b(a);

If you don't want this automatic conversion, then supply keyword "explict" for
the constructor so that it stops from such automatic conversions.

If you think, I have answered to your question then don't forget to close this
thread.

Regards,
Girish.

Hello,

Thanks for your reply.

[weaknessforcats]

This is not correct:

If you don't want this automatic conversion, then supply keyword "explict" for
the constructor so that it stops from such automatic conversions.

The example is an explicit conversion. Explicit means that onlt the programmer can call the constructor aand i this example the programmer has called the constructor.

Explicit constructors means that the compiler can't call the constructor. You use explicit constructors when you don't want he compiler calling constructors.

[bhadrisn]

This is not correct:


The example is an explicit conversion. Explicit means that onlt the programmer can call the constructor aand i this example the programmer has called the constructor.

Explicit constructors means that the compiler can't call the constructor. You use explicit constructors when you don't want he compiler calling constructors.

In what scenarios EXPLICIT keyword should be used. ????

[weaknessforcats]

Suppose you have a container with a constructor that has an int argument that is intended to create a container of a specified size:

[code=cpp]
MyContainer<int > obj(100);
[/code]

Let's suppose this contstructor creates room for 100 ints.

Then suppose you have a function like this:

[code=cpp]
void fx(MyContainer< int> arg)
{

};
[/code]

If you call this function with an int. The MyContainer constructor will be called and an empty container will be passed to the function.

[code=c]
fx(1234); //creates a MyContainer with room for 1,234 ints.
[/code]

The above is the implicit call to the constructor. In fact, this is an error. The 1234 should not be used with fx(). So, you make the MyContainer constructor explicit and then you will get a compile error on fx(1234).